## Section: Research Program

### Probability and information theory

Participants : Nicolas Bordenabe, Konstantinos Chatzikokolakis, Thomas Given-Wilson, Sardaouna Hamadou, Yusuke Kawamoto, Catuscia Palamidessi, Marco Stronati.

Much of the research of Comète focuses on security and privacy. In particular, we are interested in the problem of the leakage of secret information through public observables.

Ideally we would like systems to be completely secure, but in practice this goal is often impossible to achieve. Therefore, we need to reason about the amount of information leaked, and the utility that it can have for the adversary, i.e. the probability that the adversary is able to exploit such information.

The recent tendency is to use an information theoretic approach to model the
problem and define the leakage in a quantitative way. The idea is to consider
the system as an information-theoretic *channel*. The input represents the
secret, the output represents the observable, and the correlation between the
input and output (*mutual information*) represents the information leakage.

Information theory depends on the notion of entropy as a measure of uncertainty. From the security point of view, this measure corresponds to a particular model of attack and a particular way of estimating the security threat (vulnerability of the secret). Most of the proposals in the literature use Shannon entropy, which is the most established notion of entropy in information theory. We, however, consider also other notions, in particular Rényi min-entropy, which seems to be more appropriate for security in common scenarios like one-try attacks.